As a new type of sweetener, sucralose is a kind of chlorinated sucrose. It is 600 times sweeter than sucrose, and does not participate in the human metabolism. Sucralose has shown high safety and strong ability of anti-acidolysis. All of these advantages make sucralose to become a most popular and strong sweetener in the market. Up to the present, it has been approved for use in more than thirty countries. Studies on the synthesis of sucralose began from 1970s. Current syntheses of sucralose mainly include methods of mono-group protection and omni-group protection, of which the latter has not been commonly used because of its low yield and complicated operation. Many studies refer to the method of mono-group protection, such as U.S. Pat. No. 4,889,928, U.S. Pat. No. 5,449,772, CN1453284 and CN1526716, which have focused on the synthesis of sucrose-6-acetate with only a little study on the follow-up chlorination and alcoholysis.
U.S. Pat. No. 4,977,254 has disclosed a reaction of chloro-sulfoxide with a catalytic amount of benzyl tri-ethyl ammonium chloride in DCE, and the yield of this reaction is only 21%. European patent No. EP0043649 has disclosed a reaction of chloro-sulfoxide with pyridine in chloroform at 75° C. Since the reaction condition is too critical, it is difficult to reach in the production. Moreover, pyridine is toxic and in a bad odor. Most of the present chlorination processes need to be conducted in a high temperature, and has a serious charring phenomenon and a low yield. In the prior art, sodium methoxide was used in the alcoholysis of sucralose ester, e.g., in CN1453284 A, and there exists a problem of incomplete reaction.
In this invention, chlorination can be conducted under mild conditions with a conversation rate of over 80%. The general yield is about 50% after the crystallization. In most studies (such as CN1453284 A), sodium methylatesodium methoxide has been used as a catalyst in the alcoholysis of sucralose easter, but the disadvantage is that it can not be reacted completely. In this invention, we use KOH as a catalyst in the alcoholization in methanol solution at a proper temperature, to enable a complete reaction without creating any foreign materials.